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Peak height related variability in peak height imbalance. (Dr. William Shields, SUNY, Syracuse)Since a DNA sample usually consists of intact cells, the level of DNA present from a given contributor is generally constant. Numerous studies have shown that the signal associated with each allele in a given location should be roughly equivalent. General practice has found that "[t]he peak height ratio, as measured by dividing the height of the lower quantity peak in relative fluorescence units by the height of the higher quantity allele peak, should be greater than approximately 70% in a single source sample" (Butler Forensic DNA Typing).A constant imbalance ratio may fall below the majority of observed peak height ratios in any given study, but it does not necessarily reflect a true threshold of imbalance. A constant threshold fails to take into account the possibility of greater variance near the baseline. Exploring the behavior of heterozygotes at various RFU levels may better understand the potential variance in a single source sample. The peak height ratio consistent with a potential imbalance can change depending on the amount of DNA in a sample. A sliding threshold may assist analysts in more accurately identifying mixtures in their routine casework. MaterialsPresentationHolt CL, Buoncristiani M, Wallin JM, Nguyen T, Lazaruk KD, Walsh PS. TWGDAM validation of AMPFlSTRTM PCR amplification kits for forensic DNA casework. Journal of Forensic Sciences. 2002; 47(1). Leclair B, Fregeau CJ, Bowen KL, Fourney RM. Systematic analysis of stutter percentages and allele peak height and peak area ratios at heterozygous STR loci for forensic casework and database samples. Journal of Forensic Sciences. 2004; 49(5). |
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